A developing embryo faces the difficult task of concocting myriad tissue types — including skin, bone and the specialized glop that makes up our internal organs and immune system — from essentially the same set of ingredients: immature, seemingly directionless stem cells. Although some of the important players that provide direction to this transformation are known, it’s not been clear exactly how they work together to accomplish this feat. Now, researchers at the Stanford University School of Medicine have identified a key regulatory hierarchy in which proteins called morphogens control gene expression by directing the looping of DNA in a cell. This looping brings master regulators called transcription factors in contact with specific sets of genes necessary to make particular tissue types.